Aided by the fact that both NBC's Tonight show with Jay Leno and Late Show with David Letterman were both in reruns most of the week and that a top-rated three-hour season finale of the bachelor gave it a solid lead-in on Monday, ABC's Nightline handily beat Letterman last week and came within 200,000 viewers of unseating Leno as well, according to ratings figures released Thursday by Nielsen Media Research. In fact, Nightline did indeed beat both Letterman and Leno among adults 25-54 on Monday night when both aired new shows.